This invention relates to a vacuum holder, and more particularly, to a vacuum holder adapted to pick up a plurality of semiconductor wafers one after another for their transfer.
FIG. 1 illustrates conventional vacuum holder 10. This vacuum holder 10 comprises cup-shaped chuck 12 and suction pipe 14 so as to pick up semiconductor wafer 16. Suction pipe 14 is fitted to chuck 12 in communication with the inner space of recess 18 and connected to a vacuum pump (not shown). In operation, the vacuum pump sucks air from the atmosphere near recess 18 through suction pipe 14, and chuck 12 is moved to cover semiconductor wafer 16. When chuck 12 is brought sufficiently close to semiconductor wafer 16, the air close to chuck 12 is decompressed, thereby causing semiconductor wafer 16 to be pulled close to chuck 12. Semiconductor wafer 16, thus picked up, is carried to a desired position together with vacuum holder 10 by means of a transport mechanism (not shown).
Conventional vacuum holder 10 has the drawbacks that semiconductor wafer 16 easily gets cracked when chuck 12 picks up semiconductor wafer 16. The occurrence of cracks can be minimized, for example, by decreasing the decompressing capacity of the vacuum pump. However, the decompressing capacity of the vacuum pump should necessarily be substantially reduced in order to reliably suppress the cracking of semiconductor wafer 16. However, if the decompressing capacity of the vacuum pump is excessively reduced, chuck 12 may fail to reliably pick up semiconductor vafer 16. Namely, some semiconductor wafers remain unpicked.